1. Field of the Invention
The invention is related to the field of wafer process verification, and in particular, to verifying processes for fabricating ground connections for electrostatic discharge (ESD) resistors in magnetic heads.
2. Statement of the Problem
Wafer fabrication is a procedure composed of many repeated sequential processes to produce electrical circuits, devices, components, etc. One type of device formed through wafer fabrication is magnetic heads. Magnetic heads are used to write to magnetic recording disks and to read from magnetic recording disks, such as in a hard disk drive. Magnetic heads typically include a read element and a write element. The structure of a read element includes a first shield, a magnetoresistance (MR) sensor formed on the first shield, and a second shield formed on the MR sensor. The MR sensor may comprise a Giant MR (GMR) sensor, a Tunneling MR (TMR) sensor, or another type of MR sensor. If the read element is being operated in a current perpendicular to plane (CPP) fashion, then the first shield and the second shield are electrically connected to opposing surfaces of the MR sensor to act as current leads for a sense current that is injected perpendicularly through the MR sensor.
The MR sensor is sensitive to electrostatic discharge (ESD) damage, which may occur during the manufacturing process. Once the MR sensor is damaged, the MR sensor may not show any indication until the magnetic head is assembled and tested. Damage from an ESD event may cause the performance of the MR sensor to be below specification, or may cause an early failure in the MR sensor during operation. The prevention of ESD damage to the MR sensor is a manufacturing goal, as it increases the yield of the magnetic heads and reduces costs of manufacture.
One method of ESD protection of the MR sensor comprises connecting resistors from the first shield and second shield to a ground connection, herein referred to as an ESD protection circuit. The resistors operate to dissipate any accumulated charge that may build up on the first shield and second shield by transferring the stored charge to the ground connection. This reduction of stored charge proximal to the MR sensor is desired to reduce the possibility of an ESD event causing damage to the MR sensor.
The ESD protection circuit may fail if an inadequate ground connection is fabricated. With an inadequate ground connection, the resistors connected to the first shield and the second shield of the MR sensor will not operate to dissipate charge stored on the shields to the ground connection. This may cause charge to accumulate, leading to an ESD event and damage to the MR sensor.
It would therefore be desirable to effectively and efficiently test the quality of the ground connections for an ESD protection circuit in magnetic heads.